Generally, integrated circuits are mass produced by forming many identical circuit patterns on a single silicon wafer. Integrated circuits, also commonly referred to as semiconductor devices, are made by stacking various materials over a silicon substrate. These materials may be electrically conductive, electrically nonconductive (insulators) or electrically semiconductive. Silicon, in single crystal or polycrystalline form, is the most commonly used semiconductor material. Both forms of silicon can be made electrically conductive by adding impurities, commonly referred to as doping. Dynamic Random Access Memories (DRAMs) are integrated circuit devices comprising arrays of memory cells which contain two basic components--a field effect access transistor and a capacitor. Typically, one side of the transistor is connected to one side of the capacitor. The other side of the transistor and the transistor gate electrode are connected to external connection lines called a bit line and a word line, respectively. The other side of the capacitor is connected to a reference voltage. Therefore, the formation of the DRAM memory cell comprises the formation of a transistor, a capacitor and contacts to external circuits.
It is advantageous to form integrated circuits with smaller individual elements so that as many elements as possible may be formed in a single chip. In this way, electronic equipment becomes smaller and more reliable, assembly and packaging costs are minimized and circuit performance is improved. The capacitor is usually the largest element of a DRAM. Consequently, the development of smaller DRAMs focuses in large part on the capacitor. Three basic types of capacitors are used in DRAMs--planar capacitors, trench capacitors and stacked capacitors. Most large capacity DRAMs use stacked capacitors because of their greater capacitance, reliability and ease of formation. For stacked capacitors, the side of the capacitor connected to the transistor is commonly referred to as the "storage node" or "storage poly" and the side of the capacitor connected to the reference voltage is called the "cell poly."
The areas in a DRAM to which electrical connections are made are generally referred to as active areas. Active areas, which serve as source and drain regions for transistors, consist of discrete specially doped regions in the surface of the silicon substrate. As the size of the DRAM is reduced, the size of the active areas and the corridors available for contacts to reach the active areas are also reduced. The bit line contacts are typically formed between adjacent capacitor structures. Therefore, the chances for leakage or short circuits between the bit line contacts and the capacitor components increases as the cell spacing, and corresponding space available for the bit line contact, decreases. It is desirable to effectively isolate the bit line contacts from the capacitor components while optimizing the space available to make the contacts. The present invention addresses some of the problems associated with forming a contact corridor, typically for the contact between a bit line and an active area in the substrate, and properly aligning this contact corridor with, and isolating it from, adjacent capacitor components.